بررسي نسبت تحويل رسوب (SDR) در حوضه رودخانه جاجرود

Survey of Sediment Delivery (SDR) Ratio in Jajroud Watershed

پژوهش پيش رو، تحليل علمي و تكنيكي از بررسي مدل هاي موجود و نتايج حاصل از آن در تعيين متوسط تحويل رسوب در دوره زماني بلندمدت براي حوضه هاي متوسط‎مقياس، واقع در حوضه رودخانه جاجرود به‎منظور تعيين مناسب‎ترين مدل براي برآورد نسبت تحويل رسوب در زيرحوضه هاي اين رودخانه است. براي بررسي متوسط تحويل رسوب در دوره زماني بلندمدت، به داده‎هاي آماري بارندگي و پارامترهاي حوضه نيازمنديم. شاخص SDR شاخصي براي اندازه‎گيري واكنش حوضه به‎ميزان فرسايش بالادست است. در اين نوشتار از هفت مدل وناني، سرويس حفاظت خاك آمريكا، مانرو و رنفرو، ويليام و برنت، رويل و ويليامز براي برآورد نسبت تحويل رسوب SDR استفاده شده است. در اكثر اين مدل ها به پارامترهاي مساحت، نسبت R/L، طول آبراهه اصلي و شيب حوضه براي محاسبه SDR از طريق روابط ارايه‎شده براي هر مدل نياز است. مقادير حاصل از اين روابط براي تعيين بهترين مدل در تخمين نسبت تحويل رسوب با SDR واقعي مقايسه‎شده و مقادير حاصل از تفاضل SDR واقعي و پيش‎بيني‎شده با توجه به كمترين ميزان اختلاف، مدل مطلوب را معرفي مي‎كند. نتايج بررسي مدل هاي مذكور نشان مي دهد كه از هفت زيرحوضه مطالعه شده، در چهار زيرحوضه فشم، ميگون، امامه و افجه، مدل مانرو و رنفرو مطلوب‎ترين نتيجه را در برداشته است و در دو زير حوضه آهار و كند، مدل رويل به نتيجه مطلوب دست‎يافته و تنها در زيرحوضه لوارك، مدل رنفرو مطلوب‎ترين نتيجه را در برآورد نسبت تحويل رسوب داشته است.

Introduction Module of sediment rates in large drainage basin, has been sporadic and most of sub drainage did not module. Therefore in this scales, modeling is most effective methods in data supply for environmental decisions. Sediment delivery ratio is shortage of impure erosion that transmits from drainage in the distinct time. Data of SDR ranged from 0 to 1. This data shown county of sediment wastage in flooding time. Effective factors in SDR are: precipitation, land cover, topography, soil and relationship between them. Study area is located in northeast of Tehran, 51° 22ʹ to 51° 52ʹ E and 35° 45ʹ to 36° 50ʹ N. Methodology For computation sediment delivery ratio, area of sub basins (A) in km2 and mi2, ratio of height variance (R) to primary stream, slope of primary stream (SLP) and height difference for each sub basin has been extracted. Seven models used to assessment of sediment delivery ratio: …. . Further calculated SDR has compared with real SDR. The base of comparison in this study is variance between real and calculated SDR. Finally models that have least error, choose as best model for sub basins. Results and Discussion Results show that from seven sub basins, in Fasham, Meighon, Imame and Afjeh sub basins, Manro and Renfro models are proper and in Ahar and Kond, Roel model is most proper. The Roel model is only proper in Lovark catchment. Physiographic and hydrologic factors are effective in sediment ratio. Sediment ratio of Luvark catchment is 0.48. Whereas this catchment is not greatest catchment. This is apparent that the value of SDR in each catchment, are affected by special physiographic and hydrologic factors. SDR have a close relation with erosion. Therefore rate of moment precipitation is inevitable. Calculated SDR, have comprised with observing SDR to select suitable models. Conclusion Results of this study show that if investigated parameters using models will be closer to sediment and erosion factor, resultant from these models will have been close to reality. Also could not be use from these models in other watersheds. Because different watersheds have different qualifications. Perhaps one factor in a distinct catchment is important in SDR, but not important in the others. Therefore evaluation of models in a watershed will have been able to determine suitable model. The models must be considered in relation to genetic quality of watersheds. Physiographic, climatic and hydrologic quality of a watershed is determinant factors in suit of a model. In this qualification, we will able to select suitable model.